Telegraph hub repeater



w 9 F w N 1.. l 0 HR F V1 Dn .I SL E 0 6 e L E O 8, e ,E u@ @u VA T 0 m Mms w um AE m 6.. MMM H M WM 0R a 2 kf www Rr. R V R M, JW .5 WLI M 4 m MOR O u x R y J m B N R w L m N A A T m E E Y R E w V H H A un f (MW D P G. wn /f R G E J m T L L L AR um. um wn 8 DT mr wAa 4 wu; vu. mn 9 #nu l WW MW WM .f l 9 9 w w 6 1 6 2 l., /3 2 7 C 7 7: r c m rd m 9 g e 4 l 5 I. u n I I A F Aug. 26, 1952 Filed Dec. 29, 1948 J- R. DAVEY ET AL TELEGRAPH HUB REPEATER 5 Sheets-Sheet 2 By JJM@ Y ATTQRNEV Aug 26, 1952 J. R. DAVEY ET AL TELEGRAPH HUB REPEATER Filed Deo. 29, 1948 3 Sheets-Sheet 5 SEND/N6 HUB 7'0 OTHER SEND/NG LEGS TO OTHER RECEIVING HUH` Afan/mmm 'W Z' REA ATTORNEY REPEA TER 'atented= ug. 26, i952 W TELEGRAPH HUB REPEATER James R. Davey, New York, and Wilton T. Rea; Manhasset, N; Y., assignors to Bell Telephone Laboratories, Incorporated, New York, N; Y., a

corporation of New York Application December 29, 1948, Serial No. 67,996 n Thisinvention is an improved hub-type tele'- graph repeater. Hub-type `telegraph repeaters are well knOWnVin-the art, being described, for instance, i in^Patents 2,056,277 issuedjto` F; S. Kinkead et al."October 3,1936, 2,069,224 issued to G. C. Cummings February 2, 1937 and 2,337,496 issued tolWgT, Rea December 21, 1943. The present-improvement consists in the incorporationlinto the repeater of electronic means to perform various functions heretofore performed by electromagnetic relays andconsists particularly in an electronic control circuit tocontrol trans# mission in the sending leg of the repeater dependent on conditions imposed on the receiving leg of the repeater and on the hub. i "Whenwelectromagnetic relays are employed in the control circuit of a hub-type repeater, it has been found desirable, even when a regenerator is not required for reshaping and retiming attenuated ancl distorted signals, to employan electromagneticrelay repeating device to interconnect the receiving andisending hubs.- One of the reasonsvvhich` dictateslthe employment; of this device forl this `purposeis the necessity for introducing a delay beforesignals are impressed-on the sending legs of-the individual repeaters connected to the hubyso as to insure that the electromagnetic elements in the control circuits interconnecting theV receiving and sending hubs willV have sui cient ytime taoperate so as to perform their control functions, that is, to either lock the sending legfof.. they home individual repeater against resending its` own signals, or to unlock it if it has been locked-"and,` when required, to transmit signals incoming `fromanother repeater. When electronicfdevices are -employed to perform these functions their operation isso fast-that it is not necessarylto `employ the electromagnetic 4relay repeater Vas it is not necessary -tointroduce a delayi A repeating device is employed between the receiving and sendinghubs of an electronic hub repeater only at certain hub concentration pointsinlawidesprefad network when it is necessary to reshape and retime the signals and for this purpose -a-A regenerative repeater which may be electromagnetic, but preferably is electronic, is employed. -There is an obvious saving as a result of the elimination ofV the ordinary electromagnetic repeating relay between -the receiving and sendin'ghub both in-rst cost and maintenance expense, but,` and what is moreimportant, the elimination'of Athe extraelectromagnetic repeating deviceat most" of the hubs in a large network improvesfsignal quality byv eliminatingA the'V distuitionandbiasinevitable even inthe best elecliability of "the network. t The introduction of electronic devices valso in the sending andrreceiving legs `of the presentrepeeters cuts down the current which is required to be passed through the contacts off the electro`' magnetic"receivingrelays in each individual're-Y peat'er and throughjqthe contacts o1 `the ,regen-i erator when an electromagnetic regeneratonis employed,` thus increasing'the number; of, individual 'repeaters which` may `be' interconriected through a hub and greatly reducing contact troubles caused in existing hub-type :repeaters by the fbreakingfof contacts carrying relatively' heavy current. Y j A feature of the presentinvention is a hub=l type telegraph repeater having an electronic control circuiti A further feature of the present invention vis a hub-type telegraph repeater havingan electronic control circuit which includes 'arnultij-i vibrator or flip-flop'electronic device to dis-f` criminate between various transmission condi# tions impressed on the receiving leg of an-in" dividual repeater and on the hub soas'to prop--vr erly control transmission through the 'various sending legs of the individual repeaters connected to the hub.

- A further :feature of 4theinventionis an elec-A tronic device in the sending leg of the individual repeaters which is controlled mutuallyby conditionsV impressed on the device cuit and by Ithe hub. f e U A further feature ofthe invention is a rectifier blocking device in the receiving `leg of eachiirn-i dividual repeater connected to the "hub, whichaids in the control of potentials applied to the" electronic control `circuit interconnecting the rereivingand sending legs, inthat it keeps condi-A tions in the receiving leg independent of those on the-hub but not vice versa.

A further feature of the Vinvention is va doublel space` by-pass` arrangement incorporated in the electronic control circuit of an individualA repeater through'potential discriminating means in Athe control circuitthus eliminating the need fora separate double space by-pass circuit as presently known'in thefart. As arranged herein the double 7 space by-pass feature elects the transmission ofAjj mutilated signals to all parties connected to the network including the simultaneously sending `parties as an indication` of an abnormalwcondiff" tion, thus serving as asupervisory signal.

bythe control cir@ 2. 'Iransmission toward the hub .over one of the,

two legs and from the hub over lthe other;

3. Directional control of transmission to prevent the reflection of incoming signals;

4. The double space by-pass function;

5. Multiway regeneration by means of-aoneway regenerator unit.

Vittigention,is,also called tothe fact that by connect'ng the two leads together locally at the vcon.,- trol Vcircuitl and extending them to the switchboard as a single lead allof theforegoing functionsexcept the fifth may be exercised.

A `further feature of the invention therefore is anindividual repeater which may be interconnected ,toY ahub by means of two leads only and allor the functions required of the various leads interconnecting individual repeaters to hubs, inclndingv double spacebyfpass may be performed by means vof but two leads.

Since thedouble space Icy-pass feature is includedrinreach individual leg,.fullduplex operationbetween two facilities may be attained by means of the double spaceby-pass feature.

These and other features of the invention will beI made apparent from. the following descriptionAwhen read with reference to the vassociated drawings which show four hub circuits with electroniccontrols each of which includes av multivibrator-orniiip-flop circuit as the essential contrgl element. It is to be understood that the inv ention isnot limited to incorporation in embodiments r.disclosed herein but may be incorpo-V ratedvinotherv embodiments which will readily be suggested t those skilled in the art by the present dilcsure- Y f In thcdrawnss:

Fig. 1 is an electronic hub repeater circuit havingaa rectifier in the form of a varistor blocking th which space discharge devices are arranged as a .unipa-flop circuit to control transmission in the sending leg of the repeater; andA Figs.` 2, 3 and 4 are electroniclhub repeater circuits each having a space discharge rectifyingv deviceA serving as the blocking device in the receiving leg, and having a control circuit in which spacedischarge devices are arranged as a flipop circuiti which controls transmission in the sending leg.. of the repeater and in which other, space discharge devices are arranged to provide dividual, repeater, and a control circuit, the elements intermediate the two horizontal paths in each individual repeater; v The/ receivinglegs of allv` vecfeiving leg and having a control circuit individual repeaters are connected together through a common point or hub, shown as av vertical line, designated receiving hub at the right of Fig. 1. The sending legs of all individual repeaters are also connected together through a common point or hub, designated sending hub at the right ofFig. 1. Ify regenerationisnot required the receiving hubsand sendingA hubs are directly interconnected so that electricallyv all of the receiving legs and all of the sending legs may then be considered to be interconnected through a single common point or hub. If regeneration is required a regenerator is interconnectedvdirectly between the receiving and sending, hubs. Each, of the short horizontal spurs onstraps connectedto the receiving hub simulates the receiving leg of another individual repeater which may be connected to the hub. Similarly each, of the short horizontal spurs or straps connected to the sending hub simulates the sending legof another individual repeaterwhichmaybe connected to the hub.

In Fig. 1, if a regenerative. repeater ist) be interconnected between. the receiving andV send;- ing,` hub, switches, I0 .and I I. are actuated togen:l gage contacts I2l and.r` I3, re'sp ective1yso, as to. interconnect the regenerative repeater between the hubs. If no regenerative repeater is required switches I0 andy II are actuated, to engagegcen tacts I4 and I5 so that in effect thevreceiving andsending hubs and all of the directintercon-.f nections thereto constitutel a single; electricalpoint or hub.

Each ofthe individualu repeaters vhas aref ceiving relay, relaysv It,A I'I and I3 in repeaters I, 2 and,3,lrespectively, bymeans-of whichsignais incomingfrom a, connected line 4,5 and-6,; respectively, mayY befimpressed on the'associated receiving legnandthrough the legato the hubuand.- from the hub, eitherwith `or without regenerar tion, Vas required, on the individual ,sendingglega and ultimately onthe individual, sendingrelays I9, Z and 2l, respectively, 4whichinlpress.them in turnen the-outgoing ,linesL 8 and 9. This., will bedescribedin detail hereinafter. V

When signalsvare` received from any incomev ing line, theyv are repeated throughtherhubto.` all -sendingl legs simultaneously. However; since it is important that incoming transmission signals; should not be repeated by thesendingrelayinthe. same` individual v. repeaterxfrom which.V they are.; beingreceivedthe control circuit in'anyine dividual repeater', operatesdnzresponse tothe.- operation of its associated receiving. relay in thati repeater to prevent retransmissionzby ythepsendf ingre1ay in the same repeater. How'thiszis efe-,- fected will;now kbe explained.

The electromagnetic polar relays of the-syafY tem perFig. l vare. shown for ytl'lecondition which they assume whenthe system is idle or marking.` For-this condition thearmature ofeach ofithe. receivingrelaysl, II` andv I8 is in engagement. with its respective right-hand.ormarkingcon tact. Positive potential of uniformmagnitude isimpressedthrough resistances 13, 'I4 and 15, respectively, through each` receiving leg `Ewhich exetends through rectiers'fnZZ, 23 and 24, respective-u ly, to` the Vreceivinghub 83.y Positive.potential; of Ythe same magnitude is .impressed through, the top winding of'relay I32` in the regenerativerer peater, throughV resistance` 8|, contact. I3and-1 switch II to the receiving hub 83. No current flows in` these circuits yfor this. condition and. the armature of relay 82 isactuated to engage.1 with' its markingccntact, as-shown. .hyfthe effect of :biasing current flowingirompositive battery through' the bottom or biasing winding rof relay 82,.-and through resistance` 19 to ground, ,With theqarmature of relay; 82 on its `left-hand or marking` contact, positive battery' is impressed through resistance .BI, left-,hand or marking contact and armature orrelay `82, ,contact I2, switch l0 and sending hub 84, through the sending leg of each individual` repeater` on a potentiometer in each leg formed by resistancel and grounded resistance 64, resistance 62 and grounded resistance 65, and resistance 63 and grounded resistance 66, respectively, in repeaters I, 2 and `3, to the junctions ofwhich pairslof resistances the cathodes of the sending triodes 3|, 32V and `33, respectively, are connected in each sending leg. Positive battery is ,connected through the operating winding of a sending relay in each `sending leg, relays I9, 29 and 2| in the sending leg of repeaters 2 and 3, respectively, through resistances 58, 59 and 69, respectively, to the plate of sending triodes 3|, 32 and 33, respectively. Due tothe positive potential of their cathodes, triodes 3|, 32 and 33 do not conduct when the system'is inthe idle or marking condition. Current flows from positive battery through the biasing windings of'relays I9, 29 and 2| and resistances 61, 68 and 69, respectivelyto ground and itseilect, in the absence of current in the operating winding, actuates the associated armatures to engage their respective marking contacts `10, 1| and 12, as shown.

HItiwill now be assumedthat the armature of relay I8 in repeater 3 is actuated to engage with itsleft-hand or spacing contact. This makes receiving hub I83 negative. `Current flows from positive battery through the top winding of relay 82, resistance 8|, contact I3, switch receiving hub 83, through rectier24, which is of low resistance for this condition, throughthe armature and spacing contact of relay I8 and resistance 18 to negative battery energizing the top winding of relay 92 and actuating its armature to engageits right-hand or spacing contact after the lapse of an interval of delay introduced by the regenerator, which delay is well understood in the art. Afterfthe delay interval, in.- troduced bythe regenerative repeaterwhen used,

negative potential is impressed through resist- Y ance 89 and the spacingcontact and armature of relay 82 on the sending hub 84 and through the connectedrsending legs on the cathodes of sending triodes 3|, 32 and 33. Because of the delay; introduced bythe regenerator, before the nega@ tive spacing potential is impressed on the cathode of each of triodes 3 I, 32 and 33, the negative potential on the receiving hub 83 is impressed on thepotentiorneters formed by the two `resistances 34 and 31, 35 and 38 and 36 `and 39, respectively, to the respective junctions of which resistances` are connected the grids of triodes 28, 29 and 39respectively. Each of the triodes is thereby cut loif. Positive potential is connected` through resistances 46, 41 and 48 to the plates of triodes 28, 29 and 39, respectively.` As each triode is cut oi the potential of its plate rises to its higher positive value. The plates of triodes 2.8, 29 and 39 `are individually connected through resistances 43, 44 and `45, respectively, to the grids of` triodes 25, 26 and 21, respectively, which are normally biased negatively from negative battery through` resistances 49, 4| and 42, respectively. The potential of the grids of triodes 25, 26and'21 is raised and two of the three triodes, namely, triodes 25 and 26 conduct..

Triode 21, howevenis'cut off since.,itsplatis connected to negative battery through the space. ing contact `of relay |8 while the armature 0i' each of relays `I6 and .I1 remains onits marking contact. `The `cathodes of triodes 25 `and 26 are connected to ground through resistances 49 and 59, respectively, and are connected directly `in parallel with the cathodes of triodes 28 and 29, respectively. They are alsocoupled through resistances 52 and 53, respectively, `to the gridsof sending triodes 3| and 32, respectively. 1 Negative battery is connected through resistances 55 and 56, respectively, to the grids of triodesi3| and 32. When triodes 25 and 26 conduct their cathodes' become `more positive. The cathodes. of triodes 28 and29and the grids of triodes 3| and 32 also become more positive and triodes 3-I `and 32 conduct when, after an interval, the negative spacing signal appears on their respective cathodes. Current ows through the operating windings of sending relays |9 and 29 actuating theirz respective armatures to spacing and sending a spacing signal out over lines 'l and 8. i i ln the case of repeater 3, sincetriode 21 iscut off, the potential of its cathode and of the grid of triode 33 remain negative. Thespacing signal is not propagated through triode 33 and thereJ fore relay 2| remains in the marking condition. Attention is-particularly called to the fact that although the grids of triodes 3| and 32` `are conditioned almost instantly, in response to the negative spacing potential impressed on the receiving hub 83 through resistance 18 so that current would be passed through these triodes' if their plates and cathodes were at properpotentials, their cathodes are not made negative `with respeci;V to their plates when afregenerative repeater is employed until after the delay interval has elapsed. Therefore, propagation of the spacing signal through these triodes is delayed. In the caseof triode 33 the spacing signal isnever propagated therethrough since its grid is made nega# tive.

It will noW be assumed that the armature of relay. I8 is operated to reengage its marking contact. This makes the receiving hub 83 positive in` stantly and impresses a positive potential through resistances 34 and 31, 35 and 38 and 36 and 39 on their respective connected grids, After the delay interval, the regenerative repeater impresses a positive potential on the sendingV hub and on the cathodes of triodes 3|, 32 and 33.

In the case of triodes 28 and 29 each of their cathodes is madeso positive as a result of the' conduction of its respective associated triode y25 and 26, respectively, in response to thepreceding spacing signal, as described, that each of triodes 28 and 23 remains non-conducting and the respective associated triodes 25 and 26 remainconducting, so that the condition of the gzridof each of triodes 3| and 32 remains unchanged as long as transmission from relay` IB continues. Positive potentialY is locked on these grids-:by the action;v of the flip-flop circuit. The transmission of a spacing signal element through them continues for an interval until after the delay interval of the regenerative repeater elapses. Then the armature of relay 82 is returned to marking which, connects positive. battery through resistanceri to` the cathodes of triodes 3| and 32, cutting them both oi. As a result of this a spacing signal'element transmitted by triodes 3| and 32 persists until a marking signal element actually appears on the sending hub and on the cathodes of triodes gees-,sie

lie-changed t'ojand maintained neeativeito .pre-

vient .transmission therethrough, whileV the, grid Qstliode 331s; made positive, .assuming repeater 3 wasjgtlielast toftransrriit toward the hub; The grids of al1. .fother-triodes.. .such as 31. will remain lockedpostive soj that they. will all be in the cinicliiciling condition. This will bey explained mo fullyhereinaiter- Assuming.;tliatrelay I8 continues totransmit towardthehup, negative and positive spacing and marking signals arel applied. to the cathodes of triodesfil and 32 from the sending ,hub, by lvvay ofthe regenerative. repeater when it is employed, orlldirec'tly from-'the receiving hub through the sendinglhubivhen theswitches lill and Il engage contacts. I4 and .15. In responseto this, triodes 3] .and3'2 will conductand `be vcutoi to propagate tn efsignals.

In vt'hegcase of ,repeater 3.-, the .instant positive marking potential .isapplied through resistances l'if.andf3`9 to the grid of v'trioc'le vvfill, triode'illV cori-V ducts, itscathode beinginegative since triode '2T hasJoee'ncut oft". 'This lowers its-plate potential 'andthe` potentialof the grid of triode '2,1 which' thereoreremains out o'iT, 'so that the cathodesof triodeel?. and 30 andthegridof tr-iode3Z-lv re.- :nain negative. Therefore Vtriode33. remains out oifdring transmission 'of "marking and spacing signals frmits associated receiving relay lhotwithstanding the. change` in potential ofthe receiving andA sending hub. The control circuit in each individual repeater may be 'thought of as 'sensing the p oten'tial'on eac'h sijd'e'of its .associatedrectien such as rectifier "22" in repeater I. If a spacing signal exists on each .side Yof the rectifier, which is "the condition when any4 receiving relay, such as relay "H in; repeater l, transmits LaspacingsigriaL both of t'lietr'iodes in the lassociated flip-nop circuit* of repeater. l -are non-conducting. The-triode'suc-h as trio'de 2'8 is` non-conducting-because of the negative spacing'potential applied'- on its grid. TheV triode "suchas triodevi` is non-conducting notwithstanding itsr more V'posi-tive gridl potential because "its 'plate is'negative. Under this condit'iont'he grid 4of the triode such as 3l is negati-ve and 'the :triode is Vnon-conducting. Thenv when the'relay-such as relay Aleliinv repeater -I returns to-mar'king, lthe positive marking :condi-tion on` each side of therectien such as rectier2'2.; isin'e'Ecti-ve 'to change'tlie condition of -thegri'd of the triode such -as--triode 3| because, although. the'triode#s`uch f'a triode Z-'BHis--made conducting, its lowered plate potential makes thegrd 'of'.triode 25 more-negative maintaining itriode-25 out off. andfmaintainingfthe.grid of the triode such .as triodenillv negative, so no signals canzbe; transimitted through thesending leg of a repeater; the:

associated. receiving relay ofV which is transmittin'gf'toward the hub;

.I'ni order -toftransmita spacing signal through; thefsending leg of a repeater it .-is necessary that itswhomereceiving relay, suoliA :as relay||.&, be marking in which case lpositive potential istmpressedHonitheieft-iiand sidefof-.the'rectinerzsucii as 22, :and i af Inegativetwspacin'gf potential; transe. mltted fromareceiving-relay-in another repeat-.1 er, mustiexi'st on the right-.hand"sideA of-vtherec-f tifien In such casethe triode such .as triode iscut pif, thei trio de isi-ich as `vtried-e -2=5 conducts and the` potenti-allenY the cathodes: of triodesi25 andlsifbeoomepositive, makingvthe grid offthe triode,; such` astriode:i3-l',- positive and making the triode l conducting `When-everV the fcathodesof.- triyodey 3i|-is made negative. Oncethecathode of, the .trio de-lsuchl as- 28 ...is made.v positive; the-triade. isl-un'aifected ebysubsequent :posi-tive marking-'siga nais4 applied to its grid by fthe freceiving hub, and thespositive; condition ofitfhe grid of the triode suchl as 3l is maintained; while -ltra'n-smissioncon-ftin-ues: Every timelasnegativespacing signal'elemen-twappearsfon the-1cathode'efthe-triode; such as trienio-31,- the tub e.y vv-ill:` conducir..E to transmit a spacing signal which factuatesrel-ay-l I'Qfto spac ing.' Wheni 'a positive marking 1 signal element appears son thecathode Joiithe triode; such as tri'- ode-M; the-tulaeifwillibe cut ofi.V Rel-'ayy I'Q'lwill therefore loe restored 1to1 marking fby: the eiect of' current-infitsbiasin'g Win-ding Y .Doubflesnace toepas-s fea'tmfeY It vis.-;de'sirabie,z ,particularly in vc/.idesprea-d .herlfeA duplex networks .-interco nn'ected` through several hub circ-intswat Widely; sepanatedl'arge Vcenters-,1 that an'. indication be. provided.; when: two .subeA scribers` send simultaneously. Oi courses it is fito be..v un'denstood,` that s it .is -not possible. .in :many: cases .to-.send .two :eiiective: messages:simultanea: yously 'throughfnalrf-duplex :repeating pointsebutLit isxdesirable .when z'such l-cond'itii'in occurs fthatthel.

. isv never. .received :and isnot :effective .to mutilate the copy being .received fa-t .distantstations .as fanV indication y that -asimultaneo-usa. sending: condition Jhas:existed. The rea-senior this that the -firstspefoe which appears atffa-.half-duplexirepeat'- ingepoint gets controlan-d' the isecond space l"loes comes `.a markv during'- the overlapping' period Whfileth'eylaoth exi-st'simultaneously. Thusone ofA the simultaneously. existing. spacing signals;v i-s-shorted. Each spacingsignallelement, sav-Lin a .short message w-iiiicliappear's on aliub While.

l another spa-ce exists yas a .portion fof anothergmessagev -passingfthroughfthe hub simultaneously. .will be shortened. As the short message nis .propagate ed through .-'severalfliubs .the .remaining portions `of the. spaces vfare similarlyshortened. .Thegresult' o is 'ithatnf-ter passing tlirouglh several hubs .all of thef-.spacin'gsignal elements.; in a short messageV tend'.- to lbecome, marking. :The markingsigna-l. elements remain marking. At .remote stations. the continuous 'smarking-.signals .producexnorelecti Thus.shortvmessagesarelost. A' single :long-space whiohis continuously .maintained as .n..breaking' signal, however, will fbemropagated. to. 'the .-most distant stati-ons.

:In order to. overcome, thesvdiiiicultyfof lost short messages, ad'oublespacebyepass circuit hashen' 9 provided heretofore as an adjunct to hub circuits particularly for use-on large networks Where the need for them obviously is greatest. Such circuits, as presently known, are arranged .as separable units which are flexibly connected to the hub at such central repeating points as require them.

One of the features of the present invention, as mentionedrabove-is la double space by-pass circuit whichis incorporated into lthe electronic control circuit. Figs. 2, 3 and 4 each includes elecrtron-i-c control circuits, the operation of which depends upon `a flip-flop circuit, which control circuits incorporate therein a double space by-pass feature. i

Figs. 2, 3 and 4, each of which shows a separate embodiment of the invention, `each shows a single individual repeater connected to a hub.` Each of Figs. 2, Sand 4 is, in this respect, generally comparable to say individual repeater I andthe hub in Fig. 1. Other individual repeaters will be connected to the hub in each instance as in the case of Fig. 1, but their illustration'is not thought to be necessary to an understanding of the invention after the description lof one such multirepeater arrangement as Fig. 1. The sending and receiving hubs in yeach of Fig-s. 2, 43 and 4 may be interconnected directly or through a regenerattive repeater as in Fig. 1. Each repeater in each of Figs. 2, 3 and 4 has a receiving leg, the upper horizontal branch and la sending leg the lower horizontal bnanch in each iigure, each leg connected to the hub at the right of each gure. In Figs. 2 and '3 the receiving relay 4and the Isending relay are illustrated, shown at the left of their respective legs in each instance. In Fig. 4 they are not illustrated. An electronic control circuit including. a double space by-pass feature is shown intermediate the sending and receiving leg in each gure.

Refer now to Fig. 2.

In Fig. 2 thegreceiving relay R is connected to 'the receiving leg through resistance |00 and through the triode |01, which is arranged as a diode by4 having its grid and plate connected in parallel, to the receiving hub |05.

During an idle period and during the reception of a marking signal element the hub |05 is maintained at positive potential, such as plus 40 volts, through its connection to the junction between resistances |03 and |04 `which are arranged as a potentiometer'between positive battery |02 and ground. Positivebattery |25, which may be for instance plus 130 volts, is impressed through marking contact |26 of receiving relay R and resistance on the cathode of tube |0I.\` The cathode of tube ||l| is thus'at a higher positive potential than the plate and the tube is therefore in thenon-conducting condition during, the idle or marking period. Negative battery, which may be for instance minus 130 volts, is impressed throughspacing contact `|2`| of .receiving relay R for the spacing condition, making tube |0| con-A ducting and4 changing the potential of the re-` ceivinghub |05 to a` negative potential, which may be for instance minus 40 volts.' The receiving relay in each other individual repeater assumed to be connected'to the receiving hub re-V mains in the marking vcondition so that each associated receiving relay and its connected cathode circuit iseiectively isolated from the hub by. itsnon-conducting diode. i

It is important, when transmission signals are l incoming from' a receiving relay in a particular repeaten'that the sending leg in the same `repeaterV 10 be blocked `and that the sending legs in all other repeaters be unblocked. In the case of the individual repeater which is assumed to be transmitting communication signals towardthe hub, negative potential is impressed, during the irst spacing interval, through resistance |06 on the grid of the left-hand portion of double triode l |2; the grid being connected also through resistance |01 to negative battery |08 to center the swing'on the grid characteristic. The left-hand triodeoi' the tube 2 is cut oil. The potential of the plate of the left-hand triode of tube I2, which is sup-1 plied from positive battery |09 through resistance H0, is made more positive and is impressed through resistance |60 on the grid of the left-e' hand triode of the double triode |36, which double triode is arranged as a direct-current multivibrator or flip-nop circuit. The grid of the left` `hand triode of tube |36 is also connected to the receiving. hub |05 .through resistance ||4 and to the plate of the right-hand triode of tubeV |36` through resistance |34, so that the Vleft--hand triode of tube |36 is under joint control of these three influences. Negative battery through ree sistances |38 and |39 keeps the swings of each 'of the triodes of double triode |36 properly centered on the grid characteristic. For this condition the left-'hand triode of tube |36 is conducting, the potential of the plate of the left-hand triode of tube |36 supplied from positive potential'l3l through resistance |32 is lowered and applied through resistance |35 to the grid of the righthand triode of double triode |36, and the righti hand triode is made non-conducting, raising its plate potential, which is supplied from` positive battery 3 through resistance |33. The increased positive potential is applied through resistance |46 to the, grid of triode |48. This maintains triode I 46 conducting. .This in turn lowers the plate potential of triode |48 which is supplied from positive battery through resistance |43. The lowered plate potential is in turn supplied through resistance |44 to the grid of tetrode |49A cutting it olf. The grid of tetrode |49 is centered by negative battery through resistance |50.` The screen of tetrode i |49 is` connected to the dis` placeable contact |54 cfa variable resistance |53 connected between positive battery and ground, so that the output of the tube, when conducting,l may be established at a current `value equalto twice the uniformcurrent through the biasing winding of sending relay |56. The effect of this it originated, is ineliectual since the jpositive potentialapplied through resistance |46 isY doin-A inant. When the armature of the receiving relay returns to its marking contact, the left-handv triode of double triode l2 conducts andits lowered plate potential is applied Vthrough resistanceul.-

to the grid of the left-hand triode of tube |36.` However, the potentialof the receiving hubl DS1-is made positive for marking and is `applied through] resistance. ||4 to the same grid. The effects hand grid ci? double triode 36 is effectiveitojmaintain; the left-hand "triode conducting and 'the rightrhand triode therefore-continuesin'the, nonco'n'ducti-'ng r'condition to :maintain `the positive locking f potential through resistance 46 :on the gridt oiitriode |48.

` 'Ilierefore. once the Apositive locking V`-potential isf :applied through 'resistance 1I46con the gridV of sending triode. |48,jitiis maintained .while transmission 1 continues 'from' thefre'ceiv'ing relay. ofithe S'am'efindividual repeaterand .the sendingirelay, such asrelay" I56,'is maintainedxin the marking condition "throughout vsuch vrtransmission Vto preventthelsignals frombeingtransmitted back from the sending .relay of, the same individual repeater in .whichheyare originating.

"The manner :in 'which ordinary transmission signals Vare transmitted :by 'the' sending relays "of fall'indi'vidual repeaters other than the individual repeater inwhich'they are originating Will'now be explained.

, In `the case. of `fall individual i: repeaters otherV thanthe one in which the signals' arezoriginating, the; receiving relaysof all suchrepeatersfwillfremain on their respectivev marking contacts vThe left-hand triodes of l-all doubletriodes,y such 7as doub1e'triode`||2, infalllsuch repeaters Will conduct, loweringthe potential impressed through rsistances such aslil. InV response to thefrst -spacingsignal elementimpressed' on hub |'0 5Y the hub Vwill, gonegative :and impressV a :negative `pot'ential'through'fthev resistance such vas resistance ||l|fin all such repeaters. The lastpreoedingrepeater which ztran'smitted toward .the "hub will haveapositiveholdingpotential applied through the resistance y-such Yas resistance |34 from the platefo'f 'the right-hand triode of double .triode |36 onthe grid'of its leftehand triode. VThis Willbe overcomeby lthe potentials fromthe other two sources mentioned: above'and? the lefthandtriode inffthiswparticular repeater'will bel made vnon-conducting.` Inthe case ofthe other repeatersfthe right-handtriodesof.the tube Isuchas tube V|36 will be conducting, so' thatvareducedfpositive potential 4will" be impressed throughl the resistances such ras' resistance |34. The associatedFleft-hand triodes of doublevtriodes |36 in suchrepeaters will remain inthe non-conducting. condition. Thus theleft-handtriode of -doubleftriode |36-inall repeaters other than thatvassociated with the-repeater which is l.now starting-'to transmit toward thefreceivinghub will be in the non-conducting conditionland` the associated right'hand triode of each will `be conducting, lowering Athe -potential impressed through-resistance |46. y"This removes the'block in eachrsuchsending leg. The'seriding triode|i48 in each. such-sendinglegwillzbe made responsive therefore .to the signals ,impressed thereonffrom the sendinglhu'b. For` each. negative sending impulse :received from thesending Thub, triode, M8 :in each-such .repeater'will be cutoff. This-.will effect the actuationof .the'armature of relay?r tin each `such legtoxengagegits.spacing contact in a manner which should be understood fromtheforegoing.

When, .two spacing signals appear isimultane# uslyaongrec'eivinghub i015 itspotential is made more: negative for vinstance minus .65 1 volts, by reasonof thee-:fact'that-when two 'receivinglegs are. connected .intparallel :between megative ltbattery :|299 assumed :tothe 'min11s1130fvoltsLand thev receivingzhub, the combined resistance ofthe legsV 12 and :the .potential dropptherethrough is. reduced. The .grid ofthe rightfhandrtriode ofdobletriode |2 is. corinectedto the:receiving'hubthrouglr re.l sistance 3. The :cathode: of the' v'right-hand* triode of double :triodel I2, Jwhichisfconnectedto junction- |29. in-the. potentiometer.; formed by .resistances ||6 to I9, inclusive, connected between negative battery Yand; ground is normally` maintained Aata potential `of minus y50 `volts,forfin stance, Whichis between theA normal spacing potentialo'f the hubof minus 40voltsfand'th'e double spacing i potential zof z the fhub .of minus `65 volts. The right-hand: triode ofdoubleitriode- 2' conducts-for .the :marking condition andordinary single spacing condition of the receiving hubfl. Howevenfor the double spacezconditicn itisima'de non-.conducting l'and fthe Vpositive rswing *of `Y`its platefor this conditionis impressed throughre-4 sistance |41 -on kthegrid oftetrode |49; ".The'effect of fthispositive swing .isrmade equal to'l'the positive swingoffthe plate :of triode |48 whenfa spacingisignal is impressed. on triodelld. Tetrode 49 therefore respondsto a double space in the -same manner' asfor a'single space. z-However, the double spacerconditionpasses a spacethrough tetrode 49 around the lock vwhich isbeingaapplied to the .triode 4sirenas triode-Hsin' theltwo individual-.repeaters rrwhich` the two-,spacing signals are originating and ipasses the space vas 'well through 'all'tetrodes corresponding ato tetrode |49 in `:all receiving legs. Furthenit isappliedIinstantly in response to a double space. There-isno' delay tending :to: make' eachsecondly appearing spacing. signal :element marking during .-the;overlap periodi and there .is no. inversion. The .result is that whenever ptwo..spaces Yappear simultanecus1y,-.a ,spacing signal is propagated 'instantly from the f receiving:v hub fthrough the. rightehand triode of double triode I2 and .through tetrode |49 to the sending relay in all individual-.repeaters, including the sending relays in `the two 'repeaters .from .the receiving. relaysv of which the signals arebeing simultaneously transmitted toward vthehub and which .sending relayswvould ordinarily' be locked :by the action of their. respective flip-flop circuits. Attention isf.ca-lled` to the fact that thespacing :signals transmitted' from the sending relays 4of -the t-wo repeaters which should'be locked will each be equalinlength Ato they overlap period oftheir existence on` theV hub. In the case ofother'repeaters the spacingsign'als will be. lengthened'because a. spacing signal will start tobe transmitted bysuchrep'eaters in the regular `manner when theV first spacing Vsignalelementappears. The spacing signalY will .be ,transmitted by. means ofthe doubleSpace'featurewhile the signal-.elements actually overlap or existen the :receiving :hub simultaneously. II'hen the spacingY signal, if. one is present 'on the :hub after the simultaneous spacing iconditicm terminates, willbetransmitted inthe regul'arvmanner. It would Vbe possible for instance` to have "the j first two spacing -signal `elements .of `a train o'f'three spacing signal elements in a particular multiel'ement V,perrmitation signal combination pass through thehub .before .therstofa .train of three others rappears on the .hub .to interfere.

The V,result would be .the vtransmission .of fivel successive spacing signal Y elements, vand ingeneral transmissionlisfgarbled Aasia vresult of Y.the :translation of multielement- :permutation :codezsignalf combinations dening particularlettersioroperational `functions of .the ,teletypewriterintoother lettersand! or functions.A .This servesfat fall :ref

f 13 ceiving stations in the systemas an indication of the simultaneous sending condition.

As may be understood from the foregoing, the double spa-ce by-pass feature is not required at all' hub points particularly on single hub net'- works. It may be effectivelyv cut out of circuit by actuatingV switch |29 to engage .contact |30.'

` The double space b'y-pass 'feature `is disabled when the control circuit is to be associated with a station loop repeater which is not equipped with a break feature.` Disabling the double space by-pass feature causes the control circuit to providea break feature,jsince a spacing signal outgoing from the loop will force a 'marking signal to be vapplied to the loop. The alternative to `disabling the double space by-pass feature is to employ a loop repeater equipped with a break feature.` i

I If desired the duration of double space spacing signal' elements may be lengthened by connecting a condenser timing -circuit comprising condenser |10, resistance |1| and switch |12 to terminal |13.

Refer now to Fig. 3 which resembles Fig. 2

inthat ithas substantially the same arrange- P ment"` of receiving leg including the diode arranged triode 20| and the same transmission conditions on the leg and on the receiving hub for mark, space and double space conditions. It

includesV two triodes 202 and 203 instead of double triode |2. It has a ilip-flcpcircuit comprising` double triode 204-which resembles the iiip-op circuit in Fig. 2 and double triode |36,

respectively. It hasa triode 205 and a pentode 200 which generally resemble triode |48 and tetrode |49.

When the receiving relay R in Fig. 3 receives a spacing signal current flows through tube causing the potential of the receiving hub to go negative. The other reeciving legs are prevented from acting as positive shunts on the R hub by the diode-connected tubes in them corresponding to tube20|. "A negative potential on the receiving hub causes triode 203 to cut off. The-positive swing of `its plate potential is applied through resistance 201 to the grid ofthe right-hand triodeof double triode 204 but its effect is'overcomefkby the negative potential applied frmthe spacing contact of the receiving relay through resistance 208. Hence the grid of the right-hand triode of double triode 204 goes negative, cutting off its plate current and irnpressing an increased positive potential through resistance 209on thegrid of the left-hand triode of double triode 204. The positive swing of the plate of the right-hand triode is applied through resistance 2|0 on the grid of triode 205 `in the sending `leg overcoming the negative swing due to the spacing potential on the sending hub. This maintains triode 205 in the conducting condition, preventing the spacing signal from being transmitted through pentode 206 to the sending relay in the same repeater in which the spacing signal originated. The tube employed as tube 206 may, if preferred, be a beam power tube.

Triode 202 remains conducting during normal marking and spacing signals.

The two triodes of tube 204 and their interconnections are arranged as a flip-flop circuit. h

Once the right-hand triode of tube 204 is cut oil', inresponse to the spacing signal, as described, its raised plate potential is supplied through resistance 209 to the grid of the left-hand triode of tube 204 activating the left-hand triode. The

`lowered plate potential of the left-hand triode is in turn applied throughresistance 2|| on the grid of the right-hand triode to serve as a lock thereon and to maintain the right-hand triode` inactivated when relay Rin the same repeater returns to marking and throughout the interval while relay R in the same repeater continues to transmitl and until a corresponding relay R in some other repeater starts to transmit. Inresponse to each marking signal element transmitted from relay R in the same repeater, posi-` tive potential will be impressed through resistance 208 on the grid of the right-hand triode of tube 204 but this positive potential will not be effective. The lowered plate potential of the conducting left-hand triode supplied through resist-- ance 2|| dominates the marking potential` supplied through resistance` 208 to' maintain the right-hand triode in the cut-01T condition.: Then while transmission continues from receiving relay R in the same repeater, the sending leg wil be locked in the marking condition;

,When another repeater starts totransmit to- Ward the hub its receiving relay will be actuated to` spacing Whileall other receiving relays remain in the marking condition. Now, considering the individual repeater in Fig. 3 to simulate all repeaters in which the receiving relay remains marking while another individual repeater transmits toward the receiving'hub, the receiving hub` will become negative. Negative potential' impressed' through the resistances such as resistance 2 I2 on the grids of all triodes such as triode 203 in such repeaters cuts off thetriodes. The raised positive potential ofv their plates is irnpressed, through a resistance suchy as resistance 201 in each repeater, on the grid of the righthand triode of a double triode such as double triode 204 making the right-hand triode conducting, lowering its plate potential .and removing the lock from the sending triode 205 in-the sending leg in each such repeater. The sending-leg of each can therefore follow transmission signalsimpressed-on the hub by the singlerrepeater as-l sumed to be sending. i

When one individual repeater is transmitting toward the hub and a second sends a long space asia breaking signaler erroneously attempts to transmit a message and two spaces occur on the receiving hub simultaneously as a result, the povtentia-l of the receiving hub is mademore nega,- tive, cutting off triode 202 in every repeater conneoted to the hub, raising its positive plate potential, which is applied to the grid ofpentode 206,y making the pentode in the sending leg of each repeater conducting.` Thus, aspacing-signal element is propagated through each sendingrelay whenever a double space condition exists on the hub. The spacing `signal circumvents the ilipilop hold on sending triode 205-in `the `two repeaters which are transmitting toward the hub. Garbled signals will therefore be sent out by each sending leg connected to the hub as an indication of simultaneous sending. A long space will be sent out over each leg in response to a break signal.

Refer now to Fig. 4. This circuit is very similar to that of Fig. 3 and its method of operation the same except that when triode 302, which corresponds to triode 202 in Fig. 3, cuts oil in response to a double space, the positive potential swing of its plate is applied to the grid of the right-hand triode of double triode 304, which corresponds to double triode 204 in Fig. 3, making all the right-hand triodes conducting, particularly the one formerly locked while its receiving b freiay'i-was 4transmitting ltoward .the hub., in turn removing#Y the'positive hold fromthe grid of its associatedrtriode 305 *which v:makes .the associated triodeiSDE-asvwelliras `all other. triodes 305 respon-- sivetospacing-signals appearing on the. sending hub. Asi al'result spacingsignals are propagated to'f'all distant stations'when simultaneous'spacing signals occur :due to attempted simultaneous transmission'from' two stations or due toaspacs ing ricreativa-signal transmitted IcyV a second station whileanotheris transmitting.

The* circuits ofsFigsBand 4 are equallyieflective 'iwhenzno regenerative repeater is employed. When fone is employed the circuit of Fig. -3 is preferable for fthe following reason. The espace ing signal i in :passing through the .regenerative repeatertis subjected to the usual delay Whereas thefiipeilop control :operates almost instantly. Byithetirne Ythe delayed-spacing.'signal, dueto a, :double :space condition, haspassed through the regenerative'repeater ythe double .space con-,- ditionimay-fno longer appearv onzthe hubfsolthat triodef3ll2-will be' no 1onger effective. in removing the locklthroughthe flip=f1op tube on thesending triade Jin the two 'repeaters from4 which the Line coming spacesare beingreceived. Some tof the IVdouble.spaces; particularly overlapping: singlet elements, will' not pass through these individualirepeaters. 'Overlapping trains of 1 several 'elements vand lon'gspacing breaksigna-ls however will pass. Therefore theicir-cuit perlliig. '3 is preferable when aregenerator' is employed.

Whatis :claimed is:

-1'. In aftelegraphsystemat lea'sttwo individual hubtype'repeaters connected to a hub, individual telegraph signal transmission dev-ices insaid repeaters arrangedwtoimpress'normal transmission signals onsaid Vhubat separate'times,.isaid system subject 'at times tto `theY imposition of Vabnormal trans-mission v'signals from vmore 'than one'of said repeaters simultaneously, instrumentalities in said Arepeaters vfor producing a distinguishable potential condition on said hub While said 'ab-V normal condition prevails, an individual double space by-pass'circi'iit in each `of'said repeaters, a potential discriminating device in each of said circuits directly responsive to said potentia1 condition, and a Yseparato signal transmission control in each of said circuits for transmitting signais individually through each-of said repeaters characterizing said vabnormal condition.

'2.' A system in accordance with claim l includingan electronic control circuit in each repeater, said controlcircuit having potential discriminating controls 'for normal transmission and 1in whichisystern they double space by-pass circuit comprises an individual electronic device in each vrepeater arranged to circumvent the electronic control circuit in each repeater.

2i- :A Asystem in vee,trattienee Lwith"claim `il, iacludine en individuel electronic central circuit interconnecting :a receiving Vles A ei :seid repeaters tesetherwith the heb tewrst-eeeetrei irl a seeding les .in eeehreneetere-ndiin"wliieh seid doublelspaee bye-pass-eireuit ineaehrepeeter is interconnected betweenlsee-hub anda-seems control insaidfseridinsleemore ltemete Yfrein-,said heb -tiieniseid first eentrelsofas 4tei'dereinatessiel rst control.

4. In 'a `telesmph repeater, two transmission pethstwe eleetrenie eerltreisintereenneetins seid paths, one iiisaidY 4controls irie1ewiirigv e fpet ntie! discriminating .lock applicable between said ess t0 leostrel normal transmission. 'said leek criminetine --leetweennormal e@immuniii-:atie,np-:pel` teetiels generated in said y repeater endexterne1 to said repeater, the other of said contrtolsfin: eliidinge potentiel vdiSerenissimaeireumvention Cif-@seid leek; diserminetinsf'between-.nemereem munieetionipotenteis and fanetherfeetential, 'te eentre'l the transmission ef supervisory signals over said paths whatever the condition A.of-,said lock.

VV5 Ina hubstype teIesIeph'rePeater,'assi-nele receiving lead over lWl'iicir incoming signals are transmittedtoward the 111112,. means or impresse iris sis-nels Vfrom thel huelen-'Seid 'receiving lead. a .directional control circuit in seid frepeater for controlling the vtraI-ismiss ion ,or normal communi eationsisnals .fremseid repeetene y.deulelefspace brfpess feature infseid'reeeeter erpermittins two sim-elteneeusly existing' 'especias :signals on seid heb to'pass `.one:anletheiz and direct-:tennestiens Abetween seid :single leed 'and said-.cestini and said by-pass feature.

`6. -A hub type e repeater having eel-y ftwe -lea'ds by Ineens ei which signals ere transmitted tewerd and .iremthe-hub, :e dire `ena1xeoritrol-eirelit for eentrolline theltraesmissienef normal cem-E mueieetien "signals trein-said repeater,` a @subie speee V.intenses feature ierieerinittins ftwesi uite-rieeusly lexistiesepeeing 'signals tessili-hub fte pass ene -snetlierendvaregeeeretive :fee ure inf eerpereble :insa-id repeeter, said directional cen.- trel, Seidy ,by-Dess ffeeturesnd seid v:rege,rieretriv.e festure'eenneetee directly te said'less. Y

` JAMES iR. DAVEY.

WELT-.ON fIHfREA.

iBfEE-EBENCES @TED The following V references are of' record inthe lefof thispatent:

Number -Name Date 2;'3373886 Henley .-vr-A-r-,a-Dec. "2t, 1194.3 2,347,813 Cummings fg- Mey/,2,ir1944 

